The present disclosure relates to an apparatus and method for controlling a low voltage DC/DC converter (LDC) by using input current information on the LDC, and more particularly, to an apparatus and method for controlling the low voltage DC/DC converter (LDC) by using input current information on the LDC that may decrease an error from a topology using a transformer by using primary current information, namely, input current information on the transformer of an LDC in an electric vehicle, and use magnetization inductance information on the transformer and effective duty information on a PWM controller for controlling the LDC to enhance accuracy in controlling the LDC.
Vehicles use fossil fuel such as gasoline or diesel and have developed according to a fundamental principle in which thermal energy is converted into a physical force through an engine. However, they started finding other power sources for some reasons such as environmental problems and the exhaustion of fuel due to the usage of fossil fuel, and electric energy based vehicles such as hybrid electric vehicles (HEV), plug-in-electric vehicles (PHEV), electric vehicles (EV) have been developed.
In recent, research and development on electric components are being performed in order to produce products and preoccupy markets based on higher performance and efficiency beyond fundamental implementation.
Electric components and peripheral elements on which research and development are being mainly performed include an on board charger (OBC), a low voltage DC/DC converter (LDC), and a battery pack. Each part is a main component related directly to the power of an EV and is an element that directly affects the performance of the EV.
Among others, the LDC that receives an input voltage of 200 VDC to 450 VDC, converts the received voltage into a low voltage of 12 VDC, and supplies the low voltage to a battery and each part of the EV is one of the most important electric components in the EV.
Due to the characteristic of the LDC requiring a high voltage transformation ratio, a DC/DC converter topology (phase shifted pull-bridge) that uses a transformer is commonly used.
Typically, only a single variable, efficiency has been applied in representing the relation between an input voltage or current and an output voltage or current, and the assumption that the characteristics of physical elements configuring a circuit are all ideal has been used. When there is another variable, such an assumption may affect current control performance because errors in outputs increase. Also, such errors may limit the performance of the LDC in functions requiring current information having relatively high accuracy such as an output over current protection (OCP) function or a power limit (derating) function.
Regarding limitations due to the occurrence of errors, the LDC that shows low voltage-high current output characteristics has a limitation in that it is difficult to wind the secondary windings of a transformer several times in consideration of entire efficiency. This leads to a decrease in the magnetization inductance Lm of a transformer increasing in proportion to the number of primary windings and the transformer is no longer ideal.
Also, when a transfer ratio from an input voltage to an output voltage, effective duty Deff is not considered, actual current information has an error. When excluding the winding ratio n of a transformer, the duty representing the transfer ratio of the input/output voltage has various delay times in an actual configuration. Since the duty Deff considering a decrease in duty occurring on a transfer path appears, applying it to the process of drawing an output current is needed.